precipitations in spring and autumn, rarely snow-covered 
cold winters. 
The annual pluviometry varying between 350 and 400 mm 
and a number of days of rain by year of 60 to 100 days. These 
are in general rains of short and intense duration. The 
vegetable shelter finds a handicap to its development because 
of this weak duration of precipitations, as well as the 
important sunlight that renders the capacity of ground 
stocking very weak. 
The occupation of the ground is varied and is composed 
mainly of natural vegetation, reafforestation of pine of Alep, 
cereals with fallow, culture under greenhouse, maraichage, 
fruit trees, naked terrain, framework and carrieres. The 
annual average temperature is in the order of 17 ?c. 
Watershed are characterized by frequent winds rape with a 
West- East direction . 
3. METHODOLOGY 
Each time an important rain comes across a given region of 
the country, one expects floods. To apprehend these floods, 
we will have to understand the cycle of the water and its 
various interactions with a physical medium. 
The determination of these floods for given frequencies by 
limnigraphiques measures or by hydrologic models 
simulation can inform us on the volume and the propagation 
of flood. In practice we find ahead the problem of the 
transformation of the debit in height in a transverse section 
determined by topographic conditions. 
With traditional data, the cartography of inondables zones 
are determined and delimited by inquires in situ. It 
represents information of overflows of the oueds that remain 
vague, approximate with punctual information and not horo - 
dated. 
The present work aims to show a method of utilization of the 
numerical cartography, numerical terrain models (M.N.T), 
systems based on geographical information raster and the 
transformation of data acquired by remote sensing in useful 
data in the hydrologic modelling deterministe of conceptual 
type, distributed and meshed and the transformation of 
debits in height. The visualization of zones allocated by 
floods has been made on the numerical model of the terrain 
and the land occupation chart. 
4. INTEGRATED DATA ANALYSIS 
Several authors confirm the application of remote sensing 
and geographical information system in the area of 
predictions of floods and the cartography of floods. 
The interest of the implementation of the Model 
Hydrologique mesh in the framework of this work is taken in 
to consideration by the spatio - temporal distribution of data 
géocoded by discretisation in regular squared mesh. It 
presents an analogy with the representation of data in a 
system of geographical information matrix and remote 
sensing data. 
The hydrologic modelling employed used characteristics such 
that the size of the mesh, the allocation of the ground, the 
function of production and the function of transfer are, with 
the M.N.T, the main factors to take into account and to 
manipulate with intelligence and care. The flow chart here - 
after (Fig.1) shows the principle of the hydrologic modelling 
employed in the framework of this work by the superposition 
of layers of information. 
The area of G.I.S is in full expansion in our days, whose 
heart is a database of digital and spatial reference. They are 
considered as a computer system allowing from various 
sources, to gather and organize, to manage, to analyze and to 
combine, to elaborate and to present geographically 
contributing localized information notably to manage the 
space 
  
  
  
  
  
  
LAND COVER ef stream 
t 
= 
RAINFALL water 
Fhw 
emos 
cR 
  
  
Figure 1: the principle of the hydrologic modelling by the 
superposition of layers of information. 
For this work several software have been used to prepare the 
physiographic and meteorological database necessary for the 
simulation of a drawn to scale flow of a watershed. ( Idrisi; 
Arc/Into, Hydrologic Model meshed) 
4.1 Physiographic Data 
The estimation of the physicals characteristic of watershed 
has been undertaken from cartographic data ( topographic 
map to 1/25000) and data acquised by remote sensing of the 
satellite image Landsat TM of 15 March 1993 of the region 
of arzew. 
4.1.1 Numerical Model of the Terrain and layers derived: 
A numerical model of the image terrain has been realized from 
contour lines with a resolution 100x100 m . The choice of the 
size of the mesh has been determined with the objective of our 
work and for a large discretisation. The objective is to create a 
value of altitude on each mesh. 
The utilization of an M.N.T in a Hydrologic Model meshed 
imposes the respect of a fundamental critera: It has to allow 
the flow of water uphill the endorsement.(draining). To 
remedy to this situation we have to process the minima -local 
stemming of techniques of interpolation. The operation 
92 Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 
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